Engineering Commons^™

Microstructure And Properties Of Spark Plasma Sintered Moalb Ceramics, Ting Lou

Department of Mechanical and Materials Engineering: Dissertations, Theses, and Student Research

Molybdenum aluminum boride (MoAlB) is a ternary transition metal boride which has promising aeronautic and nuclear applications. It inheres excellent properties of the binary transitional metal borides (e.g., MoB, ZrB₂) such as high melting temperature, high hardness, and thermal conductivity. Besides, MoAlB is superior to MoB because: (1) the Al element provides an oxidation resistance at high temperatures; (2) its nanolaminated structure consisting of M-B layers with alternating Al layers results in a unique damage tolerance property. In this research, polycrystalline MoAlB have been successfully synthesized and simultaneously sintered using spark plasma sintering (SPS) from molybdenum boride (MoB) …

Optimal Grading For Strength And Functionality Of Parts Made Of Interpenetrating Polymer Networks: Load Capacity Enhancement, Zhong Chen

Department of Mechanical and Materials Engineering: Dissertations, Theses, and Student Research

Uniform parts with stress concentrations or singularities are prone to failure under relatively small loads, which motivates researchers to seek methods to enhance the strength of these parts. This dissertation studies the optimization of material grading to design parts made of functionally graded interpenetrating polymer networks (FG-IPNs) to improve their load capacity.

An acrylate/epoxy IPN with variations of elastic Young’s modulus, Poisson’s ratio, and ultimate stress at failure is used for optimization of a plate with stress concentration. The grading is optimized by attaching the finite element method (FEM) solver to a general purpose bound-constrained optimizer. Two examples, a plate …

Material Evaluation: Self Damping Wire Sd/Acsr Conductor Failures, Daniel F. Weyer

Department of Mechanical and Materials Engineering: Dissertations, Theses, and Student Research

Following numerous 954 ACSR SD Wire failures from 2010 to 2012, Nebraska Public Power District (NPPD) implemented an inspection program to determine the extent of condition for this type of widely used conductor. NPPD transmission system includes over 2000 miles of this particular conductor.

Transmission line splices are installed every 15-20 spans, with failures being located in a span containing a splice. NPPD worked with Kinectrics to complete electromagnetic field inspections for three days in 2013, with retesting performed in 2015. Throughout this inspection of 54 spans of conductor, 36 were found to have deterioration and corrosion.

Over 80% of …

Wide Bandgap Organo‐Lead Trihalide Perovskites For Solar Cells, Miao Hu

Department of Mechanical and Materials Engineering: Dissertations, Theses, and Student Research

Methylammonium lead trihalide perovskite (MAPbX3, where MA is methylammonium, and X is a halide)-based solar cells have been extensively investigated recently, with a demonstrated and certified solar power conversion efficiency (PCE) exceeding 20%. To further boost the PCE beyond the Schockley–Queisser limit, tandem structured solar cells have been investigated based on integrating MAPbX3 and the lower bandgap solar cells. Although the best reported efficiency for this type of tandem cells is not close to the theoretically achievable value, mixed-halide perovskite MAPbBrxI3–x is still one of the most promising candidates as the wide-bandgap light absorber for the tandem application to match …